A good fertilizer to use on container tomatoes should have more phosphorus (the middle number in a fertilizer’s 3-number series) than nitrogen (the first number in a fertilizer’s 3-number series). Too much nitrogen can mean lots of leaves and few fruit.
Tomatoes in pots and containers require frequent watering or they will dry out. But watering leaches nutrients out of container plants. So you need to be especially vigilant to include tomato fertilizer in your container gardening plan to get best results.
When it comes to fertilizing tomatoes in pots, little and often is better than a lot, less often. Tomatoes like regular feedings of small amounts of fertilizer rather than infrequent, large doses.
Good tomatoes require a lot of nutrients. Most potting media comes with about a two week fertilizer charge, then the plants need to be fed or growth starts to slow down. Start by applying a timed-release, pelleted, fertilizer following the label directions for rate based on pot size. At about 2 weeks after planting, begin watering weekly with a soluble fertilizer.
Until the plants begin flowering, you can use a balanced fertilizer with a 1-1-1 ratio such as 20-20-20. Once flowering, change over to a high potassium fertilizer. Most fertilizers blended for tomatoes fit this description. In our program, we’ve been using a fertilizer with a 9-15-30 plus micro-nutrients analysis.
Organic growers can use a combination of fish emulsion, green sand, kelp meal and bone meal to get similar results. Be sure to increase feeding as the plants grow larger. Apply more timed-release fertilizer after 10-12 weeks. There is good research to support the inclusion of seaweed-based supplements even with a strong conventional fertilizer program.
- Add a slow-release fertilizer (like Osmocote) to your containers when planting. Nutrients will disperse over time.
- Try grass clippings. They do double duty as mulch. Apply a couple of inches to the soil surface of your containers.
- One easy way to fertilize tomatoes is to mix a small amount of soluble, balanced tomato fertilizer (like Miracle-Gro Tomatoes) into water. Fertilize and water at the same time.